The present invention relates to a catalyst to eliminate the noxious substances such as aldehydes, contained in the exhaust gases of predominantly alcohol fueled internal combustion engines. In a further aspect, the present invention relates to a process for preparing a catalyst as set forth and uses thereof.
In view of increasing energy shortages on a worldwide basis, other fuels besides those obtained from petroleum distillates are being increasingly proposed for use in operating internal combustion engines. Illustratively methanol prepared by the gasification of coal, or ethanol, prepared by fermenting biomasses or sugar canes and subsequent distillation, have already been successfully used in many countries for some time.
While partial admixture of alcohols to the normal fuels for internal combustion engines up to a concentration of 15% by volume is widely known, several countries already have carried out conversions to pure alcohol engines which illustratively are fueled only with ethanol or methanol or predominantly with alcohol in such manner with only slight additions of gasoline.
The exhaust gases resulting from internal combustion engines fueled exclusively with gasoline contain aldehydes. However alcohol fueled internal combustion engines emit quantities of aldehydes which are orders of magnitude higher. But high aldehyde concentrations in the ambient atmosphere lead not only to disagreeable odors, and to irritation of the mucous membranes, but furthermore, whether in the presence or absence of nitrogen oxides, the aldehydes may be photo-oxidized with formation of phyto-toxic substances.
Illustratively the so-called PAN (peroxiacetylnitrate CH.sub.3 CO.sub.2 ONO.sub.2), is a compound mainly responsible for the Los Angeles smog and is generated from acetaldehyde, oxygen and nitrogen pentoxide (N.sub.2 O.sub.5).
Whereas tested technology already does exist to eliminate the noxious substances which are carbon monoxide, hydrocarbons and nitrogen oxides, effective control of the aldehydes in the exhaust gases of alcohol fueled engines is less developed by current technology.
It was found especially with base metal catalysts such as those based on copper-chromium oxide that these base metal catalysts increase rather than decrease the proportion of the aldehydes when used for the treatment of exhaust fumes of an alcohol fueled engine.
Catalysts are known from the British patent documents A 2 005 149 and A 2 036 585 which consist of a matrix comprising continuous channels along a main axis and composed of flat and corrugated layers of high temperature resistant and non-scaling steel, or of a steel with a suitably resistant surface and arranged alternatingly so as to form a stack or a spirally wound body. These layers are coated with an aluminum oxide of the transition series, and the resulting coating itself is coated with a top coating of noble metals. These catalysts are suitable to purify the exhaust gases of internal combustion engines.
The European patent No. 0 075 124 discloses a catalyst for the combustion of noxious substances contained in the exhaust gases from alcohol fueled internal combustion engines. These catalysts are formed from a matrix with continuous channels along a main axis and consisting of flat and corrugated layers of high temperature resistant and non-scaling steel or of a steel with such a surface, where the layers are mounted alternatingly as a stack or are spirally wound. The layers are coated with a coating of an aluminum oxide of the transition series which may contain from 0.5 to 40% by weight of one or more earth alkali metals and/or rare earth metals in the oxide form. Palladium, as the noble metal, is then deposited on top of said coating in amounts of 0.03 to 3% by weight based on the total weight of the coating.
It has been found that this catalyst needs improvement because it was not completely satisfactory in converting the noxious substances and in start-up behavior when used as a three-way catalyst.